Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise.
If this question can be reworded to fit the rules in the help center, please edit the question.

You could say time-consuming but I think something such as a major commitment fits better. The perfect adjective isn't always available.
–
Spehro PefhanyAug 3 '14 at 17:00

There's a class of words, normally 4 letters long and stolen from German, though the typical phraseology would have you believe that they're originally French, which are often useful :-).
–
BenAug 3 '14 at 19:40

as a German native speaker, I often look for a "is" phrase like yours (because we use such phrases a lot in German). But I have come to learn that looking for an "is"-equivalent in English might often not be the best fit. Does it have to be a is-phrase? Why not just "requires a lot of work" like in your first sentence? (BTW @Ben I was not referring to your comment. Just noticed that you mention "German" and so do I - it's a coincidence)
–
chiccodoroAug 4 '14 at 6:16